Micromechanical microphones are available which convert the sound waves into an electrical signal with the aid of such a sensor element. The conventional sensor elements include a capacitor system having at least two electrodes, between which an air gap of 0.5 μm to 10 μm is situated. Ideally, one electrode is rigid while the other electrode is movable, so that it is induced to oscillate when sound waves arrive. This causes a change in the capacitance between the two electrodes in accordance with the varying sound pressure.
The quality of such a micromechanical transducer element generally depends on the immovability of the counter electrode. In practice, the counter electrode is therefore frequently provided with relatively great thickness in that it is either structured out of the carrier substrate of the transducer element, or in that it is retroactively provided with a thick layer made of epi polysilicon, for example. However, high rigidity of the counter electrode may also be achieved if the counter electrode is produced under high tensile stress. Both the structuring of the carrier substrate and the producing of high layer thicknesses or the producing of highly stretched layers is labor-intensive and correspondingly costly.
An acoustic sensor or transducer element is described in U.S. Pat. No. 6,535,460 B2. The design of this sensor element includes a substrate having a through hole, which is spanned by a diaphragm. A perforated counter element is situated above the diaphragm, at a distance therefrom, and is connected to the substrate in the edge region of the through hole. Diaphragm and counter element jointly form a capacitor, the diaphragm acting as movable electrode while the counter element constitutes the rigid electrode. Via the through hole in the substrate, sound waves are acting upon the diaphragm, which causes the diaphragm to oscillate. The movement of the diaphragm is then detected with the aid of the counter element as capacity fluctuations of the capacitor. Special measures for affixing and/or strengthening the perforated counter element are not described in U.S. Pat. No. 6,535,460 B2.